Without the shell calendar and calendar, the size of the YO circle should be used for the cover + internal text thickness plus 3 ~ 4mm, with grey calendar and calendar, the size of the YO ring should be used for the cover + internal text thickness plus 4 to 6mm.

The maximum inner diameter of the conventional YO circle is 25.4mm, or 1 inches. The material suppliers usually represent the specifications in a proportional way. The 25.4mm16 is equal, the YO circle with the inner diameter of 25.4mm is 16/16, and the other common YO circle specifications are 5/16, 6/16 (3/8), 7/16, 8/16 (16) (7/8) and so on.